Tagliafico et al.: Exploitation of Myliobatis freminvillei off the coast of Venezuela 
149 
Table 3 
Results of analysis of variance of catch per unit of effort, measured as individuals 
per trip of bullnose ray (Myliobatis freminvillei) captured in La Pared, Venezuela, 
during 2 periods, 2006-2007 and 2013, with the year and month used as sources of 
variation. An asterisk (*) indicates statistical difference at a level of significance (a) 
of 0.05. df=degrees of freedom; SS=sum 
CV=coefficient of variation. 
of squares; MS=mean 
squares; F= 
F-test; 
Source 
df 
SS 
MS 
F 
P (perm) 
CV 
Year 
2 
19.40 
9.70 
6.95 
0.004* 
0.16 
Month 
11 
21.42 
1.95 
1.40 
0.191 
0.00 
Year x Month 
22 
36.30 
1.65 
1.18 
0.281 
0.00 
Residual 
179 
249.63 
1.39 
1.39 
Total 
214 
336.16 
Table 4 
Results of analysis of variance of CPUE, measured as kilograms per trip of the 
bullnose ray ( Myliobatis freminvillei) captured in La Pared, Venezuela, during 2 
periods, 2006-2007 and 2013, with the year and month used as sources of varia- 
tion. An asterisk (*) indicates statistical difference at a level of significance (a) 
of 0.05. df=degrees of freedom; SS=sum of squares MS=mean squares; F= F- test; 
CV=coefficient of variation. 
Source 
df 
SS 
MS 
F 
P (perm) 
CV 
Year 
2 
240.7 
120.4 
3.948 
0.025* 
1.68 
Month 
11 
296.6 
27.0 
0.884 
0.514 
0.00 
YearxMonth 
22 
534.9 
24.3 
0.797 
0.641 
0.00 
Residual 
179 
5457.4 
30.5 
30.49 
Total 
214 
6705.9 
Current literature on the sex ratio of bullnose ray 
comes from only a few studies: an 8-month study from 
Brazil, in which 6 females and 2 males were ana- 
lyzed (Schmidt et al., 2012) and a 38-year study from 
North Carolina in which a 1:1 sex ratio was reported 
(Schwartz, 2011). For another species of this genus, the 
bat ray ( M . californica), Hopkins and Cech (2003) found 
that females were more common than males (21:5) in 
California. The total sex ratio of all 187 organisms ex- 
amined for our study was 4:5 (females to males), which 
indicates no significant difference between sexes and 
that spatial segregation by sex does not exist for the 
bullnose ray. However, when the data were analyzed 
over shorter time periods, significant differences oc- 
curred in sex ratios between different years (Table 
1), highlighting the importance of collecting data over 
time periods greater than 1 year. 
Future studies of the bullnose ray need to take into 
account the short, medium, and long-term population 
dynamics of this species. Our data, and previous work 
by Schmidt et al. (2012), indicate the likelihood of com- 
plex population dynamics and variable sex ratios, yet 
the data are not adequate to accurately describe the 
factors that affect sex ratios over different temporal 
scales or to provide information that is imperative for 
the management of this species. Additionally, it has 
been proposed that different sampling techniques can 
result in variable sex ratios (Hopkins and Cech, 2003). 
Therefore, bias from different sampling methods, bio- 
logically driven spatiotemporal segregation, and the 
overall mobility of elasmobranchs could hinder efforts 
to improve understanding of population-level attributes 
that create differences in the distribution of individual 
animals and observed sex ratios. 
To our knowledge, only 2 reports describe size at 
sexual maturity for this species. McEachran and de 
Carvalho (2002) suggest that males reach maturity 
between 60.0 and 70.0 cm DW, yet they include no es- 
timate for females. Gomez et al. (2010) indicate that fe- 
males reach maturity when they are greater than 58.0 
cm DW and males reach maturity when they are above 
45.0 cm DW. By comparison, our data indicate that the 
average size at sexual maturity for this species oc- 
curs at a DW of 53.3 cm for both sexes — a size that 
is slightly lower than most of the previous estimates. 
Recently, Molina and Lopez (2015) estimated that the 
